(444b) Surface Properties of Water Containing Mixtures Using Arpc-SAFT Equation of State

In the process of designing and optimizing distillation columns, and reactive distillation, in particular, the knowledge of time-depended surface properties is indispensable. For instance, the catalytic surface in the inner of a packing column gets covered by the downwards flowing liquid phase and is surrounded by the ascending vapor phase. The flow pattern and possible foam formation are determined by the surface properties of the present vapor-liquid system. Apart from precise phase equilibria models, the surface tension in-between vapor and liquid is a crucial trait.

The time-dependent interface properties of reacting mixtures only have been calculated [1,2] regarding liquid-liquid interfaces using an approach for the free mixing enthalpy and the density gradient theory (DGT) [3], where the compressibility is neglected. The current approach is aiming towards describing the vapor-liquid surface of the esterification reaction 1‑hexanol + acetic acid ⇄ water + hexylacetate, based on the PC-SAFT [4] in combination with DGT [3] in its compressive version. Mixtures containing organic substances and water are challenging to describe [5].

A newer approach by Marshall [6], so-called ARPC-SAFT aims to facilitate describing water and its mixtures by giving a better representation of the physical behavior of water. Originally, PC-SAFT does not account for the formation of tetrahedral arrangements in water. The new approach uses an associating reference fluid in the presence of water to approximate this physical behavior. In the absence of water, the equation of state is reduced to the classic PC-SAFT. This contribution discusses the performance of ARPC-SAFT together with DGT compared to the original approach of PC-SAFT regarding phase equilibria and surface properties (surface tension, density profiles, relative accumulation in the surface) for the mixtures given by the esterification reaction as a function of temperature, pressure, and composition.

References

[1] A. Danzer, S. Enders, Fluid Phase Equilibrium 499 (2019) 112240.

[2] A. Danzer, S. Enders, J. Chem. Eng. Data 65 (2020) 312–318.

[3] J.W. Cahn, J.E. Hilliard, J. Chem. Phys. 28 (1958) 258-267.

[4] J. Gross, G. Sadowski, Ind. Eng. Chem. Res 40 (2001) 1244-1260.

[5] N. Haarmann, A. Reinhardt, A. Danzer, G. Sadowski, S. Enders, J. Chem. Eng. Data 65 (2020) 1005-1018.

[6] B.D. Marshall, Ind. Eng. Chem. Res. 57 (2018) 4070-4080.